Which dinosaurs were vegetarian?

Natural History Museum clears up some misconceptions.

The skulls of early dinosaurs are helping scientists at the Natural History Museum and the University of Bristol understand how some of the earliest herbivores may have evolved different ways of eating plants. 

Contrary to popular belief most dinosaurs were plant eaters, although they are all descended from a carnivorous ancestor. Much is already known about how different dinosaurs consumed their food, but relatively little is understood about how they evolved their preferred eating styles. 

Senior author and palaeontologist at the Museum Prof. Paul Barrett says, ‘If you want to understand how dinosaurs diversified into so many different types so effectively, it’s critical to learn how they evolved to feed on a such a wide variety of vegetation in so many different ways. This diversity in feeding mechanisms set them up to dominate life on land for millions of years to come.’

The team studied five dinosaur skulls from the plant-eating group Ornithischia; Heterodontosaurus, Lesothosaurus, Scelidosaurus, Hypsilophodon and Psittacosaurus, with many of the key specimens coming from the Museum’s own collections. These five species constitute the earliest representatives of what would become the major herbivore dinosaur groups. 

Later ornithischian dinosaurs, like Triceratops and Stegosaurus, show a wide range of adaptations to eating plants yet their early relatives have not been examined properly, until now. 

How do we know how dinosaurs ate?

After CT scanning the skulls, the team reconstructed the jaw muscles using data from birds and crocodiles to help indicate where the muscles would have been. They then carried out a ‘finite element analysis’, which involves dividing the skull into thousands of individual parts (called elements). The bite force these muscles can generate is calculated based on their size and arrangement.

Each skull was then simulated to bite an imaginary object to see how the different elements respond to the applied force. These models generate heat maps showing the areas of the skull that are strongly stressed and those that are not very stressed. The results revealed that although all of these dinosaurs were eating plants, they each had different ways of doing it.

Dr David Button, lead author of the study, who conducted the work at the Museum but is now a researcher at the University of Bristol, says: “When we compared the functional performance of the skull and teeth of these plant-eating dinosaurs, we found significant differences in the relative sizes of the jaw muscles, bite forces and jaw strength between them. This showed that these dinosaurs, although looking somewhat similar, had evolved very different ways to tackle a diet of plants.”

Heterodontosaurus appears to have large jaw muscles relative to its skull size. Therefore, it can produce a high bite force, ideal for consuming tough vegetation. Scelidosaurus had a similar bite force but relatively smaller jaw muscles compared to its skull. However, these animals had a greater overall body size and could achieve a strong bite.

In contrast, the Hypsilophodon skull doesn’t have big muscles. Instead, they reoriented their muscles, to bite more efficiently but with less muscle force.

Dr Button continues: “This research helps us understand how animals evolve to occupy new ecological niches. It shows that even similar animals adopting similar diets won’t always evolve the same characteristics. This highlights how innovative and unpredictable evolution can be.”

It is custodian of one of the world’s most important scientific collections comprising over 80 million specimens accessed by researchers from all over the world both in person and via over 30 billion digital data downloads to date. The Museum’s 350 scientists are finding solutions to the planetary emergency from biodiversity loss through to the sustainable extraction of natural resources. 

The Museum uses its global reach and influence to meet its mission to create advocates for the planet – to inform, inspire and empower everyone to make a difference for nature. We welcome millions of visitors through our doors each year, our website has had 17 million visits in the last year and our touring exhibitions have been seen by around 20 million people in the last 10 years. 

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